Little boxes of powdered soup - Knorr ? Chef
Kunzle cakes
Chocolate sweets cigarettes and cigars, there were effectively sugar sticks ones too.
Fairy green bar soap
Izal Medicated Strong Toilet Tissue Paper - aka John Wayne or Badger's ar5e.
Other than 35mm most camera film sizes that were sold by Boots, Dixons, Jessops etc. e.g. 126, 110, disc
MiniDiscs and players, DAT and DCC too.
CRT TV's and monitors. While not disappeared how many people now own a stand-alone radio ?
Floppy disks 8", 5.25", 3.5" and 3" Amstrad.
ZIP disks and drives.
ST506 hard drives, are IDE still manufactured ?
Fax machines
Lucas car components and accessories
The 3V cycle light batteries have been mentioned but others sizes are No8, 1289 rectangular & 126 bell. PP9 still are available but I don't think PP7 or PP6.